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Advice: Do I need a Sub-panel?

Discussion in 'Model S: Battery & Charging' started by sgopal2, Sep 2, 2016.

  1. sgopal2

    sgopal2 Member

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    Hello,

    I've had my Model S for a little over a year now, and had a NEMA 14-50 outlet installed in my garage, and its been working wonderfully.

    We've decided to update the kitchen, and part of the plans require a dedicated circuit for a new electric oven/microwave combo (requiring NEMA 14-50 240V/40amp service), a new circuit for a wine fridge, and another circuit for some new lighting.

    Our main panel is Cutler Hammer and has 42 slots. Our house was built in 1993 and has 200 amp service coming from the electric company. Over the years we've added quite a few things (pool pump, two zone AC, etc) and now we only have 4 slots left.

    Fortunately when installing the NEMA 14-50 in the garage for the Tesla, I was anticipating that we might need a subpanel. The Tesla outlet is located pretty far away from the main panel, so I had the electrician run 4 separate cables (6 AWG each) in a conduit to a junction box in the basement near the garage. He told me that I could upgrade to a subpanel much easier later if he did this.

    The needs for the kitchen would require another 4 normal circuits (120v/15 amp) and 1 240v/40amp circuit for the oven/microwave combo. I anticipate the peak load for all of these to be no higher than 45 amps. We might be able to squeeze everything into the existing 4 slots of the main panel, but I was thinking instead of installing a sub-panel. If an electrician were to come and install a new subpanel, he would presumably take the existing 4 x 6AWG wires and use that. Then within the new sub-panel, 2 slots would need to be dedicated for the Tesla 14-50 outlet.

    My main question is this: considering the anticipated load with the new kitchen appliances, is it acceptable to have the Tesla 14-50 outlet wired off of the sub-panel instead of directly to the main panel? I guess I'm worried that the combination of the Tesla 1450 load plus the kitchen stuff might cause lots of tripped breakers.

    I've uploaded a wiring diagram and a few photos to help explain. Any advice would be appreciated. wiring diagram.jpg main panel.jpg Junction box2.jpg wiring inside junction box.jpg wiring diagram.jpg
     
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  2. BerTX

    BerTX Member

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    I'm not an electrician, so get other opinions, but...

    50 amps is the most you can put on that circuit with 6 AWG, since the charger is considered a continuous load. The wire the electrician installed is not heavy enough to get any more than that. Yes, you can put in a sub-panel, but in reality you couldn't put any other circuits coming off of it.

    If you're lucky, he put in large enough conduit to be able to pull heavier wire, so at least that would not need to be redone.
     
  3. PtG62901

    PtG62901 Member

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    Part of the answer is going to be from your local building codes. I think you are approaching the maximum for wire, but you need to check with your electrician.
     
  4. randy1077

    randy1077 Model X60 Vin 180XX. Reverved 8/11/2016

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    You need 3 AWG to that sub panel with a 100 amp breaker. 6 AWG can't charge the Tesla and turn on the appliances at the same time without tripping the 60A breaker on the main box.
     
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  5. AndreSF

    AndreSF Member

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    Not an electrician, so advice is purely theoretical, but based on some assumptions the following might be possible:

    - 60Amp breaker in the main
    - #6 Awg existing feeder to sub panel (assuming distance allows this)
    - 60Amp main breaker in sub panel
    - 4x15Amp single poles in sub for the kitchen
    - 50Amp double pole for kitchen
    - 50Amp double pole for Tesla (assuming car can be charged late at night when kitchen is not used). I would probably simply downgrade Telsa charging to 14-30, as it's still plenty in 99% of the cases to have re-charged car by morning

    But all in all, just talk to your electrician to do the right thing.

    Good luck!
     
  6. Boatguy

    Boatguy Member

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    A sub-panel doesn't provide you anymore capacity, it's just a cabling convenience. You have empty slots in your existing main panel so there is no reason to spend money on a sub-panel unless it's to make it more convenient to add a bunch of other circuits elsewhere.

    A circuit breaker just protects the wire it is connected to, they aren't going to trip unless you pull more than their rating on that individual wire/circuit.

    The capacity of the wire is a function of both it's size AND the wire run length; more length may need a larger wire to support a given level of current. You don't mention how far the main panel is from the proposed outlet.

    Keep in mind that you've only got 200a to work with. If the pool pump, oven, Tesla, a hairdryer, etc all power up at once, you maybe over the 200a and blow your main circuit.

    Bottom line, I don't see any reason for a sub-panel, particularly since you've only pulled 6 gauge wire which won't support a 100a sub-panel.
     
    • Like x 1
  7. Barry

    Barry Member

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    Not exactly. The capacity, or current rating, is based on wire diameter only, not length. For practical purposes, you may need a larger diameter wire for a long run to keep the voltage drop below a certain level. There are wire gauge tables online that give you all this info.
     
  8. steveho

    steveho Member

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    One of the easiest may be to put a subpanel right next to your Mains. This would feed off your main box with a 100A on 2 awg CU wiring to the subpanel. The subpanel could be a 12 slot box and then you could feed all of the kitchen from that subpanel.

    In theory, i would have the Tesla in the MAIN box, as well as the oven. I'd move some smaller circuits to the subpanel.

    It would look like this:
    Do you need a sub-panel for your basement? How much will it cost?
     
  9. Xenoilphobe

    Xenoilphobe Active Member

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    I have similar loads, but decided to upgrade the main panel from 200 AMPS to 400 AMPS and then dropped a 100AMP sub panel in the garage with two HPWC's in the garage - one dialed in at 40 AMPS and the other at 80 AMPS. One car can charge anytime and other only at 1 AM. This keeps the loads in check and doesn't overload the sub panel. I could increase the other to HPWC to 80 AMPS too, but my wife hardly drives her car and 40 tops her car off in about 30 minutes to an hour.
     
  10. ernies

    ernies Member

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    Short answer: run another 200 amp feed in. You will regret it...JIMO.
     
  11. Xenoilphobe

    Xenoilphobe Active Member

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    I agree. go with a 200 AMP Subpanel just in case you end up with another Tesla. Another option is to go GAS on the oven and cooktop.
     
  12. ernies

    ernies Member

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    NOT regret a second 200 amp panel.
     
  13. steveho

    steveho Member

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    Funny everyone mentioning going with a 200A subpanel. Here in my house, I only have a 100A mains. I'm running a 90A subpanel in the garage for the future Tesla. I can't do a 200A subpanel!
     
  14. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    A 90A sub on a 100A main? You likely already have problems...
     
  15. Boatguy

    Boatguy Member

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    Thes subpanel is just a wiring convenience. The relevant issue is how many consumers, at what amperage, are running concurrently.

    Hopefully @AndrewK does not have dual chargers. If the car is pulling 80a from a 90a subpanel on a 100a main, the house is at risk.
     
  16. andrewket

    andrewket 2014 S P85DL, 2016 X P90DL (soon 100)

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    Of course. My point was that it leaves 10A for branch circuits on the main panel. I'm sure he has more than that....
     
  17. Boatguy

    Boatguy Member

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    My mistake, I should have referenced @steveho.

    It's fine for the sub-panels to sum to more than the main panel, they just can't all max out at the same time!
     
  18. ernies

    ernies Member

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    It is called "RUN A NEW SERVICE" to achieve a new 200 amp panel. Cannot imagine a 100 amp panel unless the house has not been upgraded since the 1940's.
     
  19. steveho

    steveho Member

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    My house has a 100A main, and yes I'm running a 90A subpanel to the detatched garage. I'll only wire a NEMA 14-50 to the charger, so I won't burn down the house or anything. But yes, I probably do need to replace the MAINS in the house to 200A someday. But it's not necessary RIGHT NOW for the NEMA 14-50. I'm putting the 90A in the garage because it isn't any more expensive than putting in 50A. So why not? Also I am putting in 8 circuits in the garage, but I don't really plan on a large draw except the Tesla. I'm putting in these things for future owners that may run a shop or a welder.
     

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